Properties Of Monolayers Research Articles

Effects of vacancy defects and atomic doping on the electronic and magnetic properties of puckered penta-like PdPSe monolayer: an Ab initio study

The experimental knowledge of two-dimensional penta-like PdPSe monolayer is largely based on a recent publication (Liet al2021Adv. Mater. 2102541). Therefore, the aim of our research is consequently to explore the effect of vacancy defects and substitutional doping on the electronic properties of the novel penta-PdPSe monolayer by using first-principles calculations. Penta-like PdPSe is a semiconductor with an indirect bandgap of 1.40 eV. We show that Pd and Se vacancy defected structures are semiconductors with band gaps of 1.10 eV and 0.95 eV respectively. While P single vacancy and double vacancy defected structures are metals. The doping with Ag (at Pd site) and Si (at P site) convert the PdPSe to nonmagnetic metallic monolayer while the doping with Rh (at Pd site), Se (at P site) and As (at site Se) convert it to diluted magnetic semiconductors with the magnetic moment of 1µB. The doping with Pt (at the Pd site), As (at the P site), S and Te (at Se site) are indirect semiconductors with a bandgap of ∼1.2 eV. We undertook this theoretical study to inspire many experimentalists to focus on penta-like PdPSe monolayer growth incorporating different impurities and by defect engineering to tune the novel two dimensional materials (PdPSe) properties for the advanced nanoelectronic application.

Theoretical calculations of the optoelectronic properties of a penta-graphene monolayer: study of many-body effects

Theoretical calculations of the optoelectronic properties of a penta-graphene monolayer: study of many-body effects

GeC monolayer: A promising 2D material for reusable SO2 and NO2 gas sensor with high sensitivity

Gas sensors are crucial in various fields such as environmental monitoring, industrial production, and healthcare due to their ability to detect harmful gases in real-time. This study investigates GeC monolayer as a potential material for gas sensors targeting sulfur-containing toxic gases (SO2, H2S, SF4) and nitrogen-containing toxic gases (NO, NH3, NO2). The electronic and adsorption properties of GeC monolayer were explored using density functional theory (DFT) calculations. The adsorption of SO2 and nitrogen dioxide significantly affects the band structure and work function of GeC monolayer, indicating that compared to other toxic gases, GeC monolayers exhibit higher sensitivity and selectivity towards SO2 and NO2. The electron localization function analysis indicates that the adsorption process is characterized by physical adsorption. In addition, GeC monolayer exhibits good desorption behavior towards SO2 and NO2 at room temperature. These findings suggest that GeC monolayer is a promising material for developing efficient gas sensors for detecting SO2 and NO2.

Effect of strain on thermoelectric properties of 2D SiH monolayer for solar cell and renewable energy applications: A First-Principles study

The structural, electrical, optical, and thermal characteristics of SiH monolayer were assessed using first-principles based calculations. The SiH monolayer is a semiconductor by nature and we found that the energy band gap remains zero by applying (-10%, -5%, -2%, 0%, 2%5%, 10%) different orders of strain into this material. The optical characteristics of SiH are examined for photon energies between 0 and 10 eV and electrical, thermal, Seebeck coefficient, and power factor against temperature (300˚ K 800˚ K) is reported. SiH monolayer has theoretical power conversion efficiencies up to 20%. SiH monolayer under consideration is appropriate for photovoltaic and optoelectronic applications, according to their electrical, optical, and thermoelectric characteristics.

Strain-bandgap quasi-linear correlation applied to modulation of NiBr2 monolayer optical properties

Recently, two-dimensional transition metal dihalides have shown diverse applications in spintronics, quantum devices, and optoelectronic devices. In this work, density functional theory (DFT) is adopted to investigate the effect of biaxial strain upon the electronic structure and optical properties of NiBr2 monolayer. The results show that NiBr2 is an indirect semiconductor with band gap 2.62 eV (DFT + U) and 3.18 eV (HSE06), which could vary quasi-linearly from 2.73 eV to 1.71 eV modulated by biaxial strain (6 % to −10 %). Combined with the analysis of the density of states (DOS), the primary reason for the alteration in the band gap is that strain significantly affects the behavior of Ni 3d electrons. When the strain changes from positive to negative, the DOS of Ni 3d shifts towards the Fermi level, resulting in a reduction in the band gap. Within this strain range, all of the optical properties exhibit a quasi-linear tendency similar to the band gap variation. The optical peaks of NiBr2 under compressive strain are not only red-shifted into the visible light (VL) region but also significantly enhanced in the VL and ultraviolet (UV) regions. Applying strain can greatly boost the electrical and optical properties of NiBr2 monolayer, making it a promising candidate in the field of ultraviolet detectors.

Piezoelectric, Thermoelectric, and Photocatalytic Water Splitting Properties of Janus Arsenic Chalcohalide Monolayers.

In this study, we systematically investigate the piezoelectric, thermoelectric, and photocatalytic properties of novel two-dimensional Janus arsenic chalcohalide monolayers, AsXX' (X = S and Se and X' = Cl, Br, and I) using density functional theory. The positive phonon spectra and ab initio molecular dynamics simulation plots indicate these monolayers to be dynamically and thermally stable. The mechanical stability of these monolayers is confirmed by a nonzero elastic constant (C ij ), Young's modulus (Y 2D), and Poisson ratio (ν). These monolayers exhibit strong out-of-plane piezoelectric coefficients, making them candidate materials for piezoelectric devices. Our calculated results indicate that these monolayers have a low lattice thermal conductivity (κl) and high thermoelectric figure of merit (zT) up to 1.51 at 800 K. These monolayers have an indirect bandgap, high carrier mobility, and strong visible light absorption spectra. Furthermore, the AsSCl, AsSBr, and AsSeI monolayers exhibit appropriate band alignment for water splitting. The calculated value of the corrected solar-to-hydrogen conversion efficiency can reach up to 19%. The nonadiabatic molecular dynamics simulations reveal the prolonged electron-hole recombination rates of 1.52 0.98, and 0.67 ns for AsSCl, AsSBr, and AsSeI monolayers, respectively. Our findings demonstrate these monolayers to be potential candidates in energy-harvesting fields.

Strain-dependent electronic, mechanical and piezoelectric properties of ZrSiO3 2D monolayer: A first principle approach

This study investigated the mechanical stability, elastic anisotropy, electronic and piezoelectric properties of ZrSiO₃ 2D monolayer subjected to varying degrees of strain. The monolayer films were characterized under strains ranging from −6% to +6 %, and different material properties were analyzed to understand their response to mechanical deformation using density functional theory with the Quantum Espresso code. The calculated values of cohesive and strain energy revealed that the material exhibited a symmetrical response to tension and compression within a strain value range of −2% to +2 %. Electronic properties showed strain-induced modifications: the band gap of the material decreases under tensile strain and increases under compressive strain. The material remained mechanically stable and ductile under the applied strain range of −6% to +6 %. Present investigations conveyed the modifications produced by strain on elastic anisotropy and piezoelectric characteristics of the material, finding their applications in strain-sensitive sensors, actuators, and energy-harvesting devices.

Novel two-dimensional CS semiconductor with tunable fantastic electronic and optical properties

First-principles calculations are addressed to study the stability, electronic and optical properties of the CS monolayer. It's found that the CS monolayer has excellent stability and semiconductor characteristics (Indirect band gap of 2.09 eV). Through applying external biaxial strain (−4%∼+4 %), the value of the indirect band gap of the CS monolayer is tuned in a wide interval (0.18–2.86 eV). The electronic and optical properties of the CS monolayer are also regulated by chemical modifications, exhibiting rich changing behaviors. Interestingly, the fully hydrogenated CS monolayer exhibits a wide direct band gap (3.61 eV), while the semi-hydrogenated CS monolayer exhibits an indirect band gap (3.11 eV), both have good stabilities. The absorption spectrum of the CS monolayer is found to have strong absorption in green light (528 nm) and ultraviolet light. While those of the chemically modified CS monolayers show strong absorption strength in violet and medium ultraviolet light, showing potential application in ultraviolet devices.

Thermoelectric properties of monolayer GeTe with Au, Ni, and Co substrates

Since the basic thermoelectric (TE) units must be integrated on substrates to form large-scale devices, it would be more practical to study the TE properties of the TE devices with substrates. Based on the first-principles calculation and nonequilibrium Green’s function method, we comparatively investigate the TE properties of the GeTe monolayer with its leads deposited on Au, Ni, and Co substrates, which are called GeTe-X (X = Au, Ni, and Co). It is shown that in comparison with the pristine GeTe monolayer, the figures of merit ZTs of the GeTe-X are seriously changed with one ZT peak appearing near zero chemical potential. The GeTe-Au and GeTe-Ni are of higher TE performance near zero chemical potential than the GeTe-Co, indicating one can choose Au or Ni as the substrate. Moreover, we show that the TE properties of the GeTe-X are sensitively dependent on the substrate layer number, the central scattering length, and the temperature, which necessitates the synergistic optimization of the related parameters to obtain the best TE performance. This work should be an important reference for designing practical GeTe-based TE devices.

First-principles study on the differences in mechanical and optoelectronic properties between monolayer graphene and AA bilayer graphene after neutron irradiation

Two-dimensional materials are easily affected by radiation. So far, there is no work to predict the neutron irradiation effects of AA bilayer graphene. Furthermore, the differences and comparisons of various properties between monolayer graphene and AA bilayer graphene after irradiation in the approximately same neutron environment have not been reported. In this study, the neutron irradiation processes on monolayer graphene and AA bilayer graphene were simulated in ab initio molecular dynamics. The mechanical, and optoelectronic properties of monolayer and AA bilayer systems before and after irradiation were calculated using the method based on density functional theory. The results indicate that the AA bilayer system is more resistant to neutron irradiation than the monolayer system. The bandgap of the monolayer (bilayer) system after irradiation will reach the order of 0.1 eV. This article has important value in exploring the methods of radiation reinforcement technology for carbon-based devices.

Effect of Co- and Fe-doping on magnetic and optical properties of SnS2 monolayer

The magnetic and optical properties of pure, Co/Fe single- and co-doped of SnS2 monolayers are studied by using the first-principles calculation. Results show that all the doping systems are stable. The band structures of Sn15Co1S32 and the configuration I of the Sn14Fe1Co1S32 monolayers show metal behavior. While the band structure of Sn15Fe1S32 monolayer show half-metal behavior. The estimated TC value for the configuration I of the Sn14Fe1Co1S32 monolayer is bout 696.27 K. The absorption spectrums of doping systems have a red shift. The results indicate that Co/Fe doped SnS2 monolayer systems are promising candidate materials for new spintronics and optoelectronic device.

GeP3 monolayer as a promising 2D sensing materials in detecting SO2, H2S, SOF2 and SO2F2

The detection of SF6 decomposition components using gas-sensitive sensors is significantly important for characterizing internal insulation failures and assessing the operational status of SF6 gas-insulated equipment. In this paper, the adsorption properties of GeP3 monolayers for SO2, H2S, SOF2 and SO2F2 gases were investigated based on density functional theory. Four gas adsorption systems were constructed, and the adsorption mechanisms and sensing characteristics of GeP3 monolayers on target gases were investigated by calculating parameters such as adsorption energy, charge transfer, density of states, and recovery time, along with their potential application as resistive gas sensors and field-effect transistor sensors. It is demonstrated that GeP3 monolayers were suitable for the detection of SO2, H2S, SOF2 and SO2F2 gases, all of which exhibited good chemisorption with adsorption energies of −1.36 eV, −0.78 eV, −1.82 eV and −2.91 eV, respectively. The adsorption of SO2 and H2S is found to cause a significant change in the conductivity of the GeP3 monolayers, and desorption is achieved at the optimal operating temperature in only 54.428 s and 10.686 s, respectively. Also the adsorption of SOF2 and SO2F2 can make the work function of the GeP3 monolayers significantly larger. Consequently, the GeP3 monolayers have the potential to be used as a resistive gas sensor for SO2 and H2S gases, or as a field effect transistor sensor for SOF2 and SO2F2 gases. This study provides theoretical guidance for the development of GeP3-based sensors for monitoring the insulation status and operational conditions of SF6 gas-insulated equipment.

First-principles study of the valley-polarized quantum anomalous Hall effect in TiBrTe monolayers

Valley-polarized quantum anomalous Hall effect is significant for quantum information processing based on the valley degree of freedom, but its implementation in two-dimensional materials is currently challenging. Through first-principle calculations, we investigate the electronic structure, magnetic and topological properties of the TiBrTe monolayer. TiBrTe monolayer is an intrinsic ferrovalley semiconductor with an in-plane easy axis of magnetization and a high Curie temperature of 569 K. The valley polarization in the TiBrTe monolayer can be adjusted or flipped by manipulating the magnetization orientation of the magnetic atoms. The electronic correlation effect can be used to manipulate the different energy gaps of K and -K valleys. A topological phase transition occurs with increasing electronic correlation effect, and valley-polarized quantum anomalous Hall effect can be induced, which originates from the sign-reversible Berry curvature and band inversion between dx2−y2/dxy and dz2 orbitals. These results provide an avenue for the applications of valleytronic quantum devices.

Strain-tunable magnetic property of ferromagnetic square CoSe monolayer

Two-dimensional (2D) intrinsic ferromagnetic materials with large perpendicular magnetic anisotropy (PMA) and high Curie temperature have attracted extensive attention for their potential applications. However, 2D intrinsic ferromagnets prepared experimentally are still very few and most of them have low PMA and Curie temperature. Here, using first-principles calculations, we investigate the structural stability, electronic and magnetic properties of square CoSe monolayer. The calculations indicate that CoSe monolayer is ferromagnetic metal with high Curie temperature of 251.9 K and PMA of 0.825 meV/unit cell. Additionally, the effect of biaxial strain on the magnetic and electronic properties of CoSe monolayer is explored. The CoSe monolayer has strong ferromagnetism over a biaxial strain range of −5 % to 5 %. Tensile strain can induce a transition from metal to half-metal. The Curie temperature of CoSe monolayer can be enhanced under compressive strain. Tensile strain increases the magnetic anisotropy energy by 92.2 % compared with that of the unstrained system. The robust ferromagnetism as well as the regulated magnetic anisotropy and Curie temperature of CoSe monolayer provide a new direction for the development of spintronics.

Performance analysis of graphene field effect transistor at nanoscale regime

In this paper, we examine the response of charge carriers in a dual-gate graphene field-effect transistor (GFET). We have conducted an investigation into the input-output properties of both monolayer and bilayer graphene channels. Additionally, we demonstrated the relationship between surface potential and quantum capacitance using equivalent circuit modelling. We offer precise mathematical equations that define the border points separating distinct regions. These equations guarantee the continuity of the Jacobian matrix, which is crucial for the successful implementation of a circuit simulator. We can classify the current-voltage (I-V) characteristics of bilayer graphene into three distinct regions: triode, unipolar, and ambipolar. The equivalent circuit modelling findings indicated that GFETs had superior output characteristics and transconductance behavior compared to FETs. We observed a direct correlation between transconductance and gate voltage across various drain-to-source voltages.Nevertheless, with a higher gate voltage, there was a corresponding drop in the transconductance value. The threshold voltage for this dual-gate GFET is dependent on the back gate voltage. The GFET's threshold value decreased as the back gate voltage increased.

Strain-tuned electronic and valley-related properties in Janus monolayers of SWSiX2 (X = N, P, As)

Abstract Exploring novel two-dimensional (2D) valleytronic materials has an essential impact on the design of spintronic and valleytronic devices. Our first principles calculation results reveal that the Janus SWSiX2 (X = N, P, As) monolayer has excellent dynamical and thermal stability. Owing to strong spin-orbit coupling (SOC), the SWSiX2 monolayer exhibits a valence band spin splitting of up to 0.49 eV, making it promising 2D semiconductor for valleytronic applications. The opposite Berry curvatures and optical selection rules lead to the coexistence of valley and spin Hall effects in the SWSiX2 monolayer. Moreover, the optical transition energies can be remarkably modulated by the in-plane strains. Large tensile (compressive) inplane strains can achieve spin flipping in the SWSiN2 monolayer, and induce both SWSiP2 and SWSiAs2 monolayers transit from semiconductor to metal. Our research provides new 2D semiconductor candidates for designing high-performance valleytronic devices.

Effect of a fluorinated surfactant on Langmuir monolayer properties of minimal-linker gemini surfactants

A new class of carboxylic acid-terminated gemini surfactants which contain the smallest possible headgroup linker (a single bond) has recently been reported in the literature. In this current work, we have explored how Langmuir monolayers of two different alkyl tail chain length variants (n = 12, n = 16) of these surfactants, dubbed Cn-0-Cn, are impacted by mixing with a benchmark perfluorinated surfactant, perfluorotetradecanoic acid (PF). Pure PF and C16-0-C16 monolayers share similar general characteristics, yielding compact, incompressible, solid-like films at the air-water interface. In contrast, the shorter tail chain variant, C12-0-C12 forms expanded, compressible liquid-like films. While both tail chain variants formed mixed films with PF that were generally expanded in comparison with their pure components, and were also phase-separated, the extent of interactions between film components and the resulting micron-scale morphology of the mixed films were different for the two alkyl chain lengths. Overall, PF induces different packing behavior in both the systems and the observations are attributed to the difference in the dispersion forces originating from the tail chain length differences.

The first principle study on the hydrogen storage properties of monolayer and bilayer α-graphyne decorated by alkali metal atoms

Using the first-principles density functional theory, the hydrogen storage properties of monolayer and bilayer α-graphyne systems decorated by alkali metal are investigated. The results of band structure and density of state analysis indicate that alkali metal decoration enhances the chemical activity of the adsorption substrate, leading to increased H2 adsorption capacities for Li, Na and K decorated monolayer systems (15.0 wt.%, 14.5 wt.%, 10.7 wt.%, respectively). The combined action of interlayer force and decorated metal atoms results in higher H2 adsorption capacities for Li, Na and K decorated bilayer systems (17.7 wt.%, 16.9 wt.%, 13.0 wt.%, respectively), which means the bilayer graphyne structures enhance the storage capacities for decorated structures. Additionally, the Na decorated rhombus bilayer system demonstrates the highest adsorption density of H2 molecules between α-graphyne layers. Overall, alkali metal decorated monolayer and bilayer systems exhibit promising H2 adsorption potentials.

First-Principles Calculations of TiB4 and TiB5 as Anodes with High Capacity for Na-Ion Batteries.

The electrochemical properties of TiB4 and TiB5 monolayers in Na-ion batteries (NIBs) were studied by using the first-principles calculation method based on density functional theory. The TiB4/TiB5 monolayer showed excellent Na storage capacity, capable of adsorbing two layers of Na with theoretical capacities of 1176.77 and 1052.05 mA g-1, respectively. The average operating voltages of the TiB4 and TiB5 monolayers are 0.073 and 0.042 eV, respectively, indicating that they can be used as anode materials for NIBs. More interestingly, the exposed B surface not only brings a high theoretical capacity but also provides a relatively small diffusion barrier of 0.16 (for TiB4) and 0.33 eV (for TiB5), enhancing their rate capability in NIBs.

Strain engineering of electronic structure and thermoelectric properties of quasi-hexagonal fullerene monolayer

As a newly synthesized two-dimensional (2D) carbon material, monolayer quasi-hexagonal phase fullerene (qHP C60) has an excellent electronic structure and low thermal conductivity. qHP C60 attracted significant attention from scientists because it has potential applications in thermoelectric materials. Thermoelectric properties of 2D materials significantly depend on the transport of carriers (such as electrons and phonons), and strain engineering is an essential method for modulating the transport of electrons and phonons in 2D materials. However, the strain engineering method for the modulation of the thermoelectric properties of monolayer qHP C60 has not been reported yet. In the present paper, the first-principles combined with the non-equilibrium Green's function method are used to investigate the ballistic transport properties of electrons and phonons in monolayer qHP C60. The effects of temperature, chemical potential, and biaxial tensile strain on the thermoelectric transport parameters (including conductivity, Seebeck coefficient, power factor, and thermal conductivity) as well as the figure of merit (ZT) of monolayer qHP C60 are presented, compared, discussed, and analyzed. We found that monolayer qHP C60 exhibits anisotropic characteristics in electron and phonon transport properties, showcasing outstanding thermoelectric properties. The distinctive quasi-hexagonal phase fullerene network structure offers a novel platform for exploring innovative 2D thermoelectric materials in research. This study provides crucial theoretical insights to guide the designing and implementation of 2D thermoelectric materials based on fullerenes.